Method and device for the near surface, nondestructive inspection by means of ultrasound of a rotationally symmetric workpiece having a diameter that changes from section to section

ABSTRACT

A method and a device for the near-surface, non-destructive inspection by means of ultrasound of a rotationally symmetric workpiece having a diameter that changes from section to section are provided. The method and device are based on the insonification of an ultrasonic test pulse into the workpiece at a defined insonification angle and the subsequent recording of an ultrasonic echo signal from the workpiece. Echo signals that trace back to a near-surface region ROI of the workpiece are identified and evaluated. Then, a graphic representation of the surface of the workpiece is generated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/651,575, entitled “METHOD AND DEVICE FOR THE NEAR SURFACE,NONDESTRUCTIVE INSPECTION BY MEANS OF ULTRASOUND OF A ROTATIONALLYSYMMETRIC WORKPIECE HAVING A DIAMETER THAT CHANGES FROM SECTION TOSECTION,” filed on Jun. 11, 2015, which is a national stage application,filed under 35 U.S.C. § 371, of International Application No.PCT/EP2013/071287, filed on Oct. 11, 2013, and claims the benefit of,and priority to, DE Patent Application No. 102012112120.6, filed on Dec.11, 2012, each of which is incorporated by reference herein in itsentirety.

BACKGROUND

The subject matter of the present invention is a method and device forthe near-surface, non-destructive inspection by means of ultrasound of arotationally symmetric workpiece having a diameter that changes fromsection to section. In this case, the workpiece does not have aninternal cut-out. The method and the device are suited, in particular,for the inspection of a workpiece with an anisotropic sound velocity.For example, an anisotropic sound velocity is frequently observed, forexample, in forged solid shafts which can be used, for instance, in railvehicles.

Wheel sets of rail vehicles generally include one pair of wheels mountedon a rigid solid or hollow shaft. The shafts used in this case oftenhave external diameters changing from section to section, for exampledefined regions for the accommodation of functional components, such asthe wheels, anti-friction bearings or brake disks. It is obvious thatthe shafts of wheel sets of rail vehicles constitute safety-relevantcomponents that are subject to natural wear over the long life span ofrail vehicles. For this reason, their freedom from flaws has to bedetermined by means of non-destructive inspection methods not onlyduring the production of wheel sets for rail vehicle. Rather, a regularinspection with regard to freedom from flaws of all components, in thiscase particularly the wheels as well as the shaft used, is required alsoover the entire life span of a wheel set. In practices, the mostfrequent wear phenomenon observed in shafts of wheel sets of railvehicles is the occurrence of incipient cracks, i.e. crack-like fatiguefailures that start at the surface of the respective shaft. Every railvehicle operator there-fore has to provide suitable inspection methodsand devices in order to check the wheel sets of rail vehicles withregard to their freedom from flaws regularly.

Until this day, the inspection by means of ultrasound of rotationallysymmetric workpieces having diameters that change from section tosection, in particular of solid shafts of rail vehicles, constitutes aparticularly challenging inspection task. On the one hand, this is dueto the fact that, as a rule, rotationally symmetric workpieces with adiameter that changes from section to section only have few surfacessuitable for coupling in ultrasound. Furthermore, such workpieces areoften forgings. As a rule, they have an increased anisotropy of thesound velocity for ultrasound.

Moreover, the inspection of a wheel set of a rail vehicle often entailsa downtime 5 of the rail vehicle, which is directly connected to highdowntime costs due to the rail vehicle being out of service. In order tominimize them, it would be desirable to be able to inspect a fullyassembled wheel set, i.e. a wheel set with assembled bearings and/orbrake disks. If they are mounted, then an insonification from the shaftor from the end face (e.g. by means of a conical probe) is not possiblewith the inspection methods known from the prior art.

Finally, the generation of an easily interpreted representation of theresults of an ultrasound inspection obtained on a rotationally symmetricworkpiece constitutes a problem which, as far as the applicant is aware,is so far unsolved.

SUMMARY OF INVENTION

It is therefore the object of the present invention to propose a methodand device for the near-surface, non-destructive inspection by means ofultrasound of a rotationally symmetric workpiece having a diameter thatchanges from section to section, wherein the workpiece has no internalcut-out. In this case, the results of the ultrasonic inspection aresupposed to be particularly easily interpretable.

This object is accomplished by a method and a device according toembodiments of the present invention. The dependent claims dependentclaims can be freely combined with each other in any way within thecontext of what is technically feasible. However, such a combination isnot an absolute requirement.

The method according to an embodiment of the invention serves for thenear-surface, nondestructive inspection by means of ultrasound of arotationally symmetric workpiece having a diameter that changes fromsection to section. In this case, the workpiece has no rotationallysymmetric internal cut-out. To make matters simple, such a workpiecewill be referred to below as “solid shaft”. In its simplest form, themethod comprises the following process steps:

-   -   a. insonifying an ultrasonic test pulse into the workpiece at a        coupling location E at a defined insonification angle Theta,    -   b. recording an ultrasonic echo signal from the workpiece, in an        embodiment, at the insonification angle Theta,    -   c. selecting a travel time interval I depending on the sound        path W of the ultrasonic test pulse in the workpiece, the        selected travel time interval I corresponding to a preselected        near-surface region ROI (ROI: “region of interest”) of the        workpiece,    -   d. generating an echo value G by analyzing the ultrasonic echo        signal in the selected travel time interval I, and    -   e. generating a representation of the surface of the workpiece,        wherein the echo value G is depicted in the representation in a        spatially resolved manner.

Generally, the sound path W of the ultrasonic test pulse in theworkpiece is dependent on the workpiece geometry, the coupling locationE, the insonification angle Theta, the insonification direction Phi (seebelow) and on the acoustic properties both of the workpiece as well asof the ultrasonic test probe used for the generation of the ultrasonictest pulse.

The method according to the invention provides an inspection methodwhich permits displaying the result of an ultrasonic inspection of arotationally symmetric workpiece with regard to near-surface defects ina manner that is particularly intelligible to an examiner. In this case,the representation of the workpiece surface generated according to theinvention is two-dimensional, e.g. in the form of a C image, or it isspatial, with the spatial, i.e. three-dimensional representation beingused in an embodiment. It is obvious to a person skilled in the art thatthe generation of a graphic representation of the workpiece describedherein comprises both the generation of a data set representing arepresentation of the workpiece, for example in the sense of a CADmodel, as well as the actual depiction of a graphic representation ofthe workpiece on a suitable depicting unit, e.g. on a suitable display,which can be connected, for example, to a device according to theinvention.

In an embodiment of the method, a point w on the surface of therepresentation of the workpiece is assigned to the sound path W of anultrasonic test pulse in the workpiece. For example, the location of thefirst incidence of the ultrasonic test pulse on the internal workpiecesurface can in this case be used for the point w. In the graphicrepresentation of the workpiece surface, the echo value G of theultrasonic test pulse assigned to this point w is then presented in asuitable manner, e.g. by a local color or brightness coding. This isdescribed in more detail below by way of example within the context ofthe exemplary embodiment.

If the largest amplitude of the ultrasonic echo signal occurring in theselected travel time interval I is used as the echo value G, than anembodiment of the inspection method according to the invention isobtained because it can be easily technically implemented.

In another development of the method according to an embodiment of theinvention, the ultrasonic echo signal is subjected, at least in theselected travel time interval I, to a travel time-dependent or/andinsonification angle-dependent amplification. In this way,sound-attenuating effects, for example due to the geometric expansion ofthe sound field along the propagation direction, its attenuation in theworkpiece, for example due to scattering on anisotropies, as well as apossible angular dependence of the reflection of the ultrasonic testpulse on an internal boundary surface of the workpiece, can becompensated. Consequently, flaws of the same size and orientationgenerate echo signals of approximately the same size, irrespective oftheir position in the workpiece, which in turn improves even further theinterpretability of the result of the test method.

It is obvious to the person skilled in the art that the recordedultrasonic echo signal can be subjected to a suitable signalconditioning process, e.g. for improving the signal-to-noise ratio,particularly after a digitization process. For this purpose, a varietyof methods are known in prior art.

The signal-to-noise ratio can also be significantly improved if themethod steps a to d. are executed several times for a fixed couplinglocation E and a fixed insonification angle Theta and if a mean value<G> of the generated echo values G is formed. In step e., this meanvalue <G> is then shown in the representation in a spatially resolvedway.

In a development of the method according to an embodiment of theinvention, a plurality of successive ultrasonic pulses is insonifiedinto the workpiece at different insonification angles Theta. It ispossible to vary the insonification angle Theta from pulse to pulse;however, it is also possible to vary, only after a finite series ofpulses at the same insonification angle, the insonification angle for asubsequent pulse series. Thus, a mean value formation of the flawsignals to be evaluated, over a plurality of echo signals resulting froma plurality of ultrasonic test pulses coupled in at the sameinsonification angle Theta, improves the signal-to-noise ratio. In theprocess, the method according to an embodiment of the invention iscarried out for each ultrasonic test pulse insonified into theworkpiece. In another embodiment of the method, the position of thecoupling location E on the workpiece surface relative to its axis ofsymmetry S is kept substantially constant in the process. “Keptsubstantially constant” in this context means, in particular, that theposition X of an ultrasonic test probe comprising an ultrasonictransducer for generating the ultrasonic test pulses is kept constantrelative to the axis of symmetry S of the workpiece. In the case of theultrasonic test probes for oblique insonification with a variableinsonification angle commonly used in practice, in which the ultrasonictransducer is disposed, for example, on a wedge-shaped leading body, theactual coupling location changes slightly if the insonification angle ischanged. This effect is to be allowed to be neglected in this case.

So-called “phased array” ultrasonic test probes, which are known in theprior art and whose application in the context of the present inventionwill be discussed in more detail, permit an electronic tuning of theinsonification angle Theta over a broad angle range. Particularly inconnection with the embodiments of the method according to an embodimentof the invention, in which the insonification angle Theta is variedbetween different ultrasonic test pulses of a test pulse series, the useof such “phased array” test probes with an electronically tunableinsonification angle Theta has proven to be particularly advantageous.Particular advantages are obtained if, furthermore, test probes inaccordance with the teaching of the family of PCT/EP2010/0566154 arebeing used, with this teaching being added to the disclosure of thepresent application by this reference. The use of such test probesallows taking into account the curvature of the coupling surface in the35 axial and radial directions, which is advantageous in particular inthe case of shafts of wheel sets whose shaft geometries can in part alsobe curved completely in the longitudinal direction, so that at leastwith components such as wheels, bearings or brake disks mounted on theshaft—there is no purely cylindrical region with a constant diameter forultrasonic coupling.

In an embodiment, the insonification of the one or more ultrasonic testpulses into the workpiece is carried out in such a way that the soundpath W of the ultrasonic test pulse(s) in the workpiece and the axis ofsymmetry S of the rotationally symmetric workpiece span a common plane,i.e. that the sound path W of the ultrasonic test pulse(s) intersectsthe axis of symmetry S of the rotationally symmetric workpiece. Thiscommon plane is hereinafter also referred to as insonification plane P.The preselected near-surface region ROI as a rule is located behind thispoint of intersection.

In another development of the method according to an embodiment of theinvention, the relative position of the test probe position X and theworkpiece is not altered while a first part of the process of theinspection method is carried out, in which the insonification angleTheta is changed continuously. This means that the above-mentionedcondition is satisfied in this first part of the process for allultrasonic test pulses coupled into the workpiece.

Since this is a rotationally symmetric workpiece, an effectivetranssonification of the workpiece can be realized, in particular, by arelative rotation of the workpiece and the ultrasonic test probe aboutthe axis of symmetry of the workpiece, characterized by a rotation angleBeta. Therefore, in another development of the method according to anembodiment of the invention, a relative rotary movement of the testprobe and the workpiece of the above-mentioned type is realized in asecond process step, with the rotation angle Beta being at least 360°according to an embodiment. In an embodiment, the above-mentionedcondition is adhered to in the process, according to which the soundpath W of every ultrasonic test pulse coupled into the workpieceintersects the axis of symmetry S of the workpiece. The simplest way torealize a relative rotary movement of the test probe and the workpieceabout the axis of symmetry S of the workpiece is by rotating theworkpiece about its axis of rotation S under the test probe, which isheld fixed in its position X.

In an embodiment of the method, while maintaining the position of theultrasonic test probe relative to the axis of symmetry S of theworkpiece, a series of ultrasonic test pulses is insonified into theworkpiece, while the insonification angle Theta and the rotation angleBeta is varied at the same time. In this case, having gone through apredetermined interval for the insonification angle Theta, for example,a gradual relative rotary movement of the ultrasonic test probe and theworkpiece is carried out about the axis of symmetry S of the workpiece.Thus, an electronic tuning of the insonification angle Theta is possibleover an angle range of at least 30° to 60°, or of at least 20° to 75°.Subsequently, a relative rotary movement of the test probe and theworkpiece about the axis of symmetry S of the workpiece by, for example,maximally 5°, particularly maximally 1°, and more particularly maximally0.5°, is carried out. For this new relative position of the test probeand the workpiece, a series of ultrasonic test pulses is then insonifiedinto the workpiece at a varying insonification angle Theta. Then,another relative rotation of the test probe and the workpiece takesplace, etc. On the whole, the relative rotation angle Beta of the testprobe and the workpiece about the axis of symmetry S of the workpieceover a complete test cycle is to be at least 360°, in an embodiment, itis 360° or an integral multiple of 360°.

In an alternative development of the method according to an embodimentof the invention, the insonification angle Theta and the relativerotation angle Beta of the workpiece and the ultrasonic test probe aboutthe axis of symmetry S of the workpiece are varied simultaneously, withthe rotating speed of, for example, the workpiece about its own axis ofsymmetry S being selected to be so low that the result is still asufficient geometric overlap of the ultrasonic test pulses in the ROI inthe workpiece.

In another development of the method according to an embodiment of theinvention, two groups of ultrasonic test pulses are insonified into theworkpiece. In this case, the first group of ultrasonic test pulses has atravel direction which has one component in the positive direction ofthe axis of symmetry S of the workpiece. In contrast, the second groupof ultrasonic test pulses has a travel direction which has one componentin the negative direction of the axis of symmetry S of the workpiece. Inan embodiment, the first and the second groups of ultrasonic test pulsesare coupled into the workpiece at substantially the same location. Forthis purpose, it is possible, in particular, to integrate two ultrasonictransducers into a single test probe that transmit the first and secondgroups of ultrasonic test pulses. By means of this development of themethod according to an embodiment of the invention it is possible tovirtually double the tunable angle range, and thus 5 the sector of theworkpiece to be acquired from a test probe position X (relative to theaxis of symmetry S of the workpiece), which makes it possible to carryout the method with an efficiency that is increased even more.

In an embodiment, the inspection method is repeatedly carried out fordifferent test probe positions X on the workpiece surface. This thirdpart of the process serves for acquiring as large a (near-surface)volume of the workpiece as possible. As a rule, carrying out the methodat a few discrete test probe positions X is sufficient for acquiring theentire (near-surface) volume of the workpiece, even in the case ofragged workpiece geometries.

If all of the three parts of the process are run through for aworkpiece, then, for most workpiece geometries, the entire near-surfacevolume of the workpiece can be transsonified with the ultrasonic testpulses and thus inspected. The representation of the workpiece surfacegenerated therefrom according to the invention thus contains completeinformation on the result of the ultrasound inspection of the entirenear-surface volume of the workpiece. Particularly informative is thegraphic representation described herein of the result of the ultrasonicinspection method according to the invention, because a completerelative rotation of the test probe and the workpiece by 360° or anintegral multiple thereof about the axis of symmetry of the workpiecehas taken place during the inspection of the workpiece. Because themethod is furthermore carried out starting from different test probepositions X, the entire volume of the near-surface region of theworkpiece is transsonified and subsequently graphically representedprovided the rotationally symmetric workpiece has a suitable geometry.

A development of the method according to an embodiment of the inventionpermits the reduction of the process duration by effectively reducingthe amount of data to be analyzed. This is possible by limiting theevaluation of the recorded ultrasonic echo signals, which correspond to,in part, very long travel distances of the test pulse in the workpiecethat occur primarily at large insonification angles Theta, to those echosignals that result from a preselected near-surface region of theworkpiece to be inspected. Within the context of the present invention,this preselected region is also referred to as ROI (=“region ofinterest”). As a rule, the ROI to be used during the execution of themethod is determined by the examiner with knowledge of the materialproperties as well as of the geometry of the workpiece. As a rule, in anembodiment, the ROI is selected to be adjacent to that internalworkpiece surface at which a first reflection of the ultrasonic testpulse in the workpiece occurs.

The ROI can be limited, for example, to the sector of the workpiece thatextends radially inwardly, from the workpiece surface, by a few to a fewtens of millimeters, for example by 30 to 60 millimeters, or by 40millimeters.

Also, the ROI can be defined differently from section to section alongthe axis of symmetry of the workpiece, e.g. in regions with a changingshaft diameter, it can have a larger extent than in regions with aconstant diameter.

Thus, ROI can also be deliberately selected to be larger in somesections, e.g. in order to depict displays from a wheel, bearing orbrake seat possibly formed on the solid shaft.

Because of the existing uncertainty with regard to the sound velocity ina forged workpiece, it is advantageous to limit the ROI not only up tothe incidence of the ultrasonic test pulse on the internal workpiecesurface, but a certain travel time beyond, i.e. an internal totalreflection on the workpiece surface may possibly occur in the ROI.However, the ultrasound testing pulse at least reaches the internalworkpiece surface with a very good degree of certainty.

The travel time interval to be selected that corresponds to the ROIrelates to the response time between the ultrasonic test pulse beingcoupled into the workpiece and the arrival of ultrasonic echo signals.The workpiece geometry is presumed to be known, as are the acousticproperties of the workpiece. Moreover, the coupling location E of theultrasonic pulse, the insonification angle Theta and the insonificationdirection are known. For example, the insonification direction can bedefined via the inclination angle phi of the sound propagation directionwith respect to the plane defined by the axis of symmetry S and thecoupling location E. In embodiments of the method according to theinvention, the inclination angle phi is zero, i.e. the sound path W andthe axis of symmetry S of the workpiece span a common plane P. Thecoupling location E is directly linked to the test probe position X onthe workpiece surface and the insonification angle Theta. The sound pathW of the ultrasonic test pulse in the workpiece can be determined fromthis, which, when a workpiece geometry and workpiece properties aregiven, is generally a function of the test probe position X, of theinsonification angle Theta and of the inclination angle phi. Inparticular, the travel time tROI_EIN can be determined after which theultrasonic test pulse enters the ROI previously determined by theexaminer. Furthermore, a travel time tROI_AUS can be determined afterwhich the first reflection of the ultrasonic test pulse on an internalworkpiece surface has occurred. For a given insonification angle Theta,the ROI can be defined via this travel time interval I, i.e. every echosignal recorded after a response time tAntwort with2tROI_EIN≤tAntwort≤2tROI_AUS results from an ultrasound reflector (e.g.a local anisotropy in the material structure of the workpiece, the localworkpiece geometry, a flaw) in the ROI. It is obvious that the traveltime interval I is, as a rule, dependent on the given insonificationangle Theta.

In a development, the ROI is defined via the travel time interval Iselected (and thus to be analyzed) for a given insonification angleTheta. The basis is the sound velocity for the ultrasonic test pulse inthe workpiece, which can be specified only with a certain uncertainty.The start of the travel time interval I is defined by the time 2tROI_EINat which the ultrasonic test pulse hits the internal surface for thefirst time at the earliest, i.e. the highest possible sound velocity isused as a basis. The end of the travel time interval I is defined by thetime 2tROI_AUS at which the ultrasonic test pulse hits the internalsurface for the first time at the latest, i.e. the lowest possible soundvelocity is used as a basis. It is thus ensured that the ultrasonic testpulse hits the internal workpiece surface in the selected travel timeinterval with certainty, i.e. the internal surface lies within the ROIin every case.

Optionally, the travel time interval I to be analyzed, and thus the ROI,can be additionally enlarged by a defined “allowance” (e.g. ±5%, ±10%,±15%) added to the maximum or minimum sound velocity to be presumed.This constitutes an advantageous development of the above-mentionedembodiment. It can thus be accomplished that a near-surface region witha defined, in particular constant, thickness of, for example 30 to 60mm, or 40 mm and above, is always being examined.

According to the development of the method according to an embodiment ofthe invention, the analysis with regard to flaw signals Fi of theultrasonic echo signal recorded from the workpiece at the angle Theta islimited to the selected travel time interval I which corresponds to thenear-surface region of the workpiece to be inspected.

In its development, an embodiment of the invention provides a practicalmethod for an effective data reduction to an ROI to be individuallydefined by the user for the respective inspection task. This effectivedata reduction permits the use of very high pulse repetition rates inthe range of up to a few kHz and a highest temporal resolution in theanalysis of the ultrasonic echo signals. Moreover, near-surface flaws inthe workpiece can be reliably detected by means of the method and thedevice, even in the case of a ragged workpiece geometry and furthercomponents possibly mounted on the workpiece surface, wherein the methodand the device can be applied so effectively that excessively longinspection times are avoided.

In an alternative approach, which is also to be comprised by theinvention, the echo signal recorded in a time-resolved manner isdigitized substantially over a travel time interval I from the entryinto the workpiece to the double travel time until the first incidenceupon the internal workpiece surface on the side opposite from the testprobe, whereby a comprehensive raw data set is generated. This isreduced to a subset of data points to be analyzed by selecting onlythose data points whose origins lie in the previously defined ROI. Withregard to their result, both approaches lead to the selection of thesame subset of data points/echo signals to be analyzed. With regard totheir results, they are therefore to be considered as equivalent.

A device according to the invention serves for the near-surface,non-destructive inspection by means of ultrasound of a rotationallysymmetric workpiece having a diameter that changes from section tosection, wherein the workpiece has no rotationally symmetric internalcut-out. In particular, it is suitable for inspecting forged solidshafts of wheel sets of rail vehicles. A device according to theinvention comprises at least the following features:

-   -   a) a test probe (40) for insonifying an ultrasonic test pulse        into the workpiece (1) at a defined insonification angle Theta        and for recording an ultrasonic echo signal from the workpiece        (1),    -   b) a control unit (20) configured to:

control the test probe (40) for insonifying an ultrasonic test pulseinto the workpiece (1) at a defined insonification angle Theta,

-   -   ii. record by means of the test probe (40) an ultrasonic echo        signal from the workpiece (1), and, in an embodiment, at the        angle Theta,    -   iii. select a travel time interval I depending on the sound path        W of the ultrasonic test pulse in the workpiece (1), with the        selected travel time interval I corresponding to a near-surface        region ROI of the workpiece (1), and    -   iv. generate, by analyzing the recorded ultrasonic echo signal        in the selected travel time interval I, an echo value G, and    -   v. generate a representation (50) of the surface of the        workpiece (1), wherein the echo value G is depicted in the        representation (50) in a spatially resolved manner.

In particular, a device according to the invention is suitable forcarrying out the method according to the invention. In developments ofthe device, the above-described embodiments of the method according tothe invention are implemented in the control unit.

Therefore, these different embodiments in particular permit therealization of those advantages that were already discussed inconnection with the method according to the invention, to whichreference is made here.

In another development, the testing device comprises a guiding deviceconfigured to orient the test probe relative to the axis of symmetry Sof the workpiece in such a way that the sound path W of the ultrasonictest pulse in the workpiece and the axis of symmetry S span a commonplane, the insonification plane P. This means that the travel directionof the ultrasonic test pulses insonified by the test probe into theworkpiece has one component in the direction of the axis of symmetry ofthe workpiece. By ensuring the above-described travel direction of theultrasonic test pulses insonified into the workpiece using the guidingdevice, a particularly simple sound field results in the workpiece. Thissimplifies the subsequent signal processing and evaluation.

In a development of the testing device according to an embodiment of theinvention, the test probe comprises an ultrasonic transducer dividedinto a plurality of individually controllable transducer segments. Suchtest probes are known from the prior art; they are referred to as“phased array” test probes and, for example, permit the electroniccontrol of the insonification angle of the ultrasonic pulses generatedby the ultrasonic test probe into the workpiece, given a suitableelectronic control of the individual transducer segments. Ultrasonictest probes according to the teaching of the family of PCT/EP2010/056614are used with particular preference. In an embodiment, the control unitis furthermore configured to control a test probe of the phased arraytype in the aforementioned manner so that the insonification angle Thetainto the workpiece can be set electronically. Moreover, the control unitis configured to insonify by means of the test probe a series ofultrasonic test pulses into the workpiece at different insonificationangles Theta.

In another development of the testing device according to an embodimentof the invention, the latter moreover comprises a rotating device. Therotating device is configured to generate a relative movement of thetest probe and the workpiece, in such a way that the workpiece isrotated about its axis of symmetry S under the test probe. In anembodiment, the rotating device comprises a means for acquiring therotation angle Beta of the relative movement, e.g. an encoder. Moreover,in an embodiment, it is connected to the control unit of the testingdevice in such a way that the acquired rotation angle Beta of the rotarymovement can be transmitted to the control unit. In a simplifiedembodiment of this device, it is not the angle of the relative movementof the test probe and the workpiece that is actually applied by therotating device which is acquired and transmitted by the rotating deviceto the control unit. Rather, the control unit is configured forcontrolling the rotating device in such a way that the latter generatesa relative movement of the test probe and the workpiece about a rotationangle Beta predetermined by the control unit. An acquisition of theangle of the rotary movement that is actually executed does not have tobe carried out in this case, i.e. an encoder, for example, can beomitted.

In another development of the testing device according to an embodimentof the invention, the test probe of the testing device comprises twoultrasonic transducers. They are characterized in that the traveldirection of a first part of the pulses has one component in thedirection of the axis of symmetry S of the workpiece and the traveldirection of a second part of the pulses has one component orientedcontrary to the direction of the axis of symmetry S. A particularlycompact construction is provided if the two ultrasonic transducers aremounted on a common leading body, which may, for example, consist ofpolystyrene, polycarbonate or Plexiglas and can be disposed in a commontest probe housing.

Finally, the device according to an embodiment of the inventioncomprises a display unit, e.g. an LCD, connected to the control unit.The control unit is in that case configured to generate a graphicrepresentation of the workpiece on the display unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features are apparent from the dependent claims aswell as from the following exemplary embodiments. The exemplaryembodiments are to be understood not to be limiting; they serve forrendering the invention described above in a general mannercomprehensible to the person skilled in the art. The exemplaryembodiments will be explained with reference to the drawing. In thedrawing:

FIG. 1: shows a side view of a typical solid shaft of a wheel set of arail vehicle,

FIG. 2: shows a schematic representation of a test probe and a controlunit according to a first exemplary embodiment of a testing deviceaccording to the invention,

FIG. 3: shows a partial sectional representation through the solid shaftfrom FIG. 1 for illustrating the sound paths of the ultrasonic testpulses in the workpiece and the ROI,

FIG. 4: shows a diagram from which the data reduction due to theintroduction of the ROI becomes apparent,

FIG. 5: shows a C image recorded on the solid shaft section according toFIG. 3, and

FIG. 6: shows a three-dimensional representation of the solid shaftsection from FIG. 3 with detected flaws signals Fi drawn in.

DETAILED DESCRIPTION

FIG. 1 shows a side view of a typical solid shaft 1 of a wheel set of arail vehicle. It is a rotationally symmetric forging with a diameterchanging from section to section, as becomes clear from FIG. 1. Inparticular, the shaft 1 comprises different sections with a constantdiameter, which are provided for accommodating the wheel hubs, therolling bearings, with which the solid shaft is rotatably mounted on therail vehicle, and a centrally disposed brake disk. As a forging, a solidshaft according to FIG. 1 typically has a certain anisotropy of thesound velocity for ultrasound, which is produced by local structuralchanges caused by the forging process. In this case, the solid shaft 1is rotationally symmetric to the drawn-in axis of rotation S.

FIG. 2 shows a first exemplary embodiment of a testing device 10according to the invention, which comprises a control unit 20 and a testprobe 40 connected to it. The test probe 40 comprises a segmentedultrasonic transducer 42 of the phased array type. It thereforecomprises a plurality of individually controllable transducer elements(not shown). In this case, the segmented ultrasonic transducer 42 isdisposed on a leading body 44 which in turn consists of a materialsuitable for oblique insonification into a forged steel workpiece. Theleading body 44 often consists of polystyrene, polycarbonate orPlexiglas®. Generally, both the leading body 44 as well as the segmentedtransducer 42 are disposed in a common test probe housing (not shown) inorder to shield them from environmental influences. In FIG. 2, the testprobe 40 is shown placed on the cylindrical surface of a rotationallysymmetric workpiece 1, which can be, for example, the solid shaft 100shown in FIG. 1. The contact surface which is formed by the leading body44 and with which the test probe is placed on the surface of theworkpiece 1 therefore also has a hollow-cylindrical shape whose internaldiameter is matched to the external diameter of the workpiece 1. As wasalready explained in the introduction, there are a lot of differentshaft geometries that can also be completely curved in the longitudinaldirection, i.e. it is possible that the workpiece to be inspected has nopurely cylindrical region with a constant diameter. Using the technicalteaching known from PCT/EP2010/056614, the use of test probes whoseleading bodies are adapted to the cross section of the workpiece both inthe longitudinal direction as well as the transverse direction is alsopossible. This adaptation is generally effected locally, i.e. for apredetermined X position relative to the axis of symmetry S of theworkpiece.

The control unit 20 is configured for controlling the test probe 40 insuch a way that it generates an ultrasonic test pulse that is coupledinto the workpiece 1 at a defined insonification angle Theta.Furthermore, the control unit 20 is configured to adjust theinsonification angle Theta in a controlled manner. By way of example,FIG. 2 shows three sound paths of three ultrasonic test pulses coupledinto the workpiece 1 at different insonification angles Theta 1, Theta 2and Theta 3. While the insonification angles Theta 1, Theta 2 and Theta3 can be controlled with very good accuracy by the control unit 20, theentrance angles Gamma 1, Gamma 2 and Gamma 3 resulting in the workpiece1 are associated with a certain uncertainty that is directly linked tothe above-mentioned anisotropy of the sound velocity for ultrasound inthe forged solid shaft 100. It is also immediately apparent from FIG. 2that, given a constant test probe position X, the coupling location Echanges slightly if the insonification angle Theta is varied, due to therefraction during the transition into the workpiece, i.e. given aconstant position X, a different coupling location E 1, 2, 3 is obtainedfor each insonification angle Theta 1, 2, 3. If the requirements withrespect to the accuracy of the inspection are not too high, this effectcan be neglected, e.g. in determining the position w at which the soundpath W hits the internal workpiece surface for a given insonificationangle Theta and a given test probe position X. In the case of higherrequirements with regard to accuracy, it can be taken into account bycalculation, e.g. when determining the position w.

Furthermore, the control unit 20 is configured to record, by means ofthe test probe 40, an ultrasonic echo signal in a time-resolved mannerfrom the workpiece 1, and, in an embodiment, at the angle Theta, and tothen digitize it in a selected travel time interval I. In thisconnection, the control unit 20 is configured to select a travel timeinterval I depending on the sound path W of the ultrasonic test pulse inthe workpiece 1, with this selected travel time interval correspondingto a near-surface region of the workpiece 1. As was already mentioned inthe introduction, the sound path of the ultrasonic test pulse in theworkpiece is generally dependent on the workpiece geometry, the testprobe position X as well as on the insonification angle Theta and theinclination angle Phi (which was defined in the introductory part andis, in an embodiment, zero) and on the acoustic properties of theworkpiece. In particular, the control unit 20 can be configured topermit the user to autonomously define the above-mentioned near-surfaceregion depending on the workpiece geometry. In this case, thespecifically selected test probe position can also be taken intoaccount.

In an embodiment, the ROI is defined via the travel time interval Iselected (and thus to be analyzed) for a given insonification angleTheta. The basis is the sound velocity for the ultrasonic test pulse inthe workpiece, which can be specified only with a certain uncertainty.The start of the travel time interval I is defined by the time 2tROI EINat which the ultrasonic test pulse hits the internal surface for thefirst time at the earliest, i.e. the highest possible sound velocity isgenerally used as a basis. The end of the travel time interval I isdefined by the time 2tROI AUS at which the ultrasonic test pulse hitsthe internal surface for the first time at the latest, i.e. the lowestpossible sound velocity is generally used as a basis. In individualcases, deviations may result due to the workpiece geometry and thechange of travel paths W due to the change of the entrance angle Gamma(cf. FIG. 2) in the case of a variation of the sound velocity. It isthus ensured that the ultrasonic test pulse hits the internal workpiecesurface in the selected travel time interval I with certainty, i.e. theinternal surface lies within the ROI in every case.

Optionally, the travel time interval I to be analyzed, and thus the ROI,can be additionally enlarged by a defined “allowance” (e.g. ±5%, ±10%,±15%) added to the maximum or minimum sound velocity to be presumed.This constitutes an advantageous development of the above-mentionedembodiment. It can thus be accomplished that a near-surface region witha defined, in particular constant, thickness of, for example, 30 to 60mm, or 40 mm and above, is always being examined.

As mentioned above, the control unit 20 is configured to select a“near-surface” travel time interval I. Then, the control unit 20digitizes and analyzes the recorded ultrasonic echo signals in theselected “near-surface” travel time interval I with regard to flawsignals Fi, i.e. with regard to ultrasonic echo signals that indicatenear-surface flaws in the workpiece 1, such as incipient cracks or nearsurface defects. In the simplest case, only a maximum echo amplitude inthe travel time interval I is determined here, and no assessment of theecho amplitude as a “flaw signal Fi” or “no flaw signal” is made.Rather, the echo amplitude (or a similar value obtained in a morediscriminate manner) itself is considered as a flaw signal Fi, i.e.there is at least one flaw value Fi for each test probe position X, eachinsonification angle Theta and each rotation angle beta (see below).

The concept according to the invention of the selection of anear-surface region, the region of interest, is illustrated by means ofFIG. 3, which presents a partial sectional representation of the solidshaft 100 from FIG. 1. FIG. 3 shows the sound paths W of a plurality ofultrasonic test pulses that are coupled into the workpiece 1 at asubstantially constant coupling location E by means of the stationarytest probe 40 disposed at the position X on the surface of the workpiece1. In the process, the insonification angle Theta is successivelyvaried, from one ultrasonic test pulse to the next, between presetlimits, which are typically between 20 and 75°. In this way, anextensive section of the internal surface of the solid shaft 100opposite from the test probe position X or the coupling location E isscanned by the ultrasonic test pulses. For each ultrasonic test pulseinsonified into the solid shaft 100 at a certain insonification angleTheta, the test probe 40 acquires in a time-resolved manner the echosignal returning from out of the solid shaft 100 at the angle Theta. Ifthe ROI has been previously defined depending on the geometry of theworkpiece 1 to be inspected, as this is indicated in FIG. 3 by the lines11 and 12, then, given a known coupling location, it is possible forevery insonification angle Theta set by the control unit 20 to determinethe travel time tROI_EIN until the ultrasonic test pulse insonified intothe workpiece 1 at the angle Theta reaches the ROI. Due to the soundvelocity in the material of the workpiece 1, which is known per se, thistravel time tROI_EIN corresponds to a travel distance L_(ROI) _(_)_(EIN) in the workpiece, as becomes clear from FIG. 4.

FIG. 4 now shows, for the ROI defined in FIG. 3 by the lines 11 and 12,the value range I of the response time, or the travel distance L, in thesolid shaft 100 which has to be analyzed, at a given insonificationangle Theta, with regard to relevant flaw signals in order to detectsuch flaws that are situated in the ROI. By way of example, traveldistances L_(ROI) _(_) _(EIN) (=entrance ROI) as well as L_(ROI) _(_)_(AUS) (=exit ROI) are drawn in for an insonification angle Theta=35°.

Here, it is possible, at a given test probe position X, for anyinsonification angle Theta, to record the echo signal in a time-resolvedmanner for a predetermined duration I after coupling in the ultrasonictest pulse. In this case, the duration I is selected in such a way that,for the selected range of the insonification angle Theta, for theselected test probe position X, as well as for the geometry and thematerial properties of the workpiece, it is ensured that echo signalsfrom the ROI 10 are always still acquired with regard to time. Thismeans that a digitized echo signal exists for each point within the ROIshown in the diagram according to FIG. 4, which is situated between thelines 13 and 14. According to the invention, only those echo signalsfrom the ROI are examined for flaw signals Fi. Thus, the echo signals tobe evaluated are limited by the selection of echo signals that originatefrom the ROI. Therefore, the lines 11 and 12 from FIG. 3 are in thiscase translated, based on the physical laws, into the lines 13 and 14 inFIG. 4. The set of those measurement points that lie within these twoboundary lines in FIG. 4 then forms a subset of the data points to beanalyzed, which is selected according to the invention. This is obtainedin accordance with the approach of the present invention by the echosignal, which is provided for a long travel time interval, beingdigitized and analyzed only within a small window in time I.

Thus, the insight resulting from FIG. 4 is utilized already during theexecution of the ultrasound inspection. For a workpiece with knownmaterial properties and a known geometry, an ROI is defined analogouslyto the representation in FIG. 3. For a given test probe position, therelationship between the insonification angle Theta and the responsetime or travel distance in the workpiece, which is apparent from FIG. 4,is exploited in order to determine, for every insonification angleTheta, the response time interval I in which signals are to be expectedthat are to be ascribed to flaws in the ROI. For a given test probeposition X, the ultrasonic inspection is then limited to theabove-mentioned response time interval I for each individualelectronically set insonification angle Theta.

Within the context of the method according to the invention, those echosignals that can be traced back to the ROI are subsequently analyzedwith respect to flaw signals by the correspondingly configuredevaluation unit 20. For example, such a flaw analysis can be based onthe amplitude of echo signals, wherein, in this case, use can be made ofall of the methods for signal evaluation and, optionally, signalimprovement, e.g. for increasing the signal-to-noise ratio, as wasalready mentioned in the general part.

Within the context of the exemplary embodiment an echo value G isdetermined during the flaw analysis, which is then assigned to a point won the surface of workpiece 1, e.g. the location of the first incidenceof the ultrasonic test pulse on the internal surface of the workpiece 1.In this case, the uncertainty with regard to the entrance angel Gammaresulting from the uncertainty with respect to the local sound velocity,and the uncertainty with regard to the location of the first incidenceon the internal surface of the workpiece 1 resulting therefrom, is, inan embodiment, neglected. This echo value G is determined by determiningthe echo value with the highest amplitude in the selected travel timeinterval I. This maximum amplitude value is then assigned to theabove-mentioned point (location of first incidence) on the surface ofthe workpiece 1.

FIG. 6 illustrates the actual conditions in an inspection task on arotationally symmetric workpiece 1. In this case, FIG. 6 is athree-dimensional representation 50 generated according to the inventionof the shaft section of the solid shaft 100 from FIG. 1 apparent fromFIG. 3. A guiding device (not shown) is provided with which the testprobe 40 is retained on the surface of the solid shaft 100 whilemaintaining the position X (X position in FIG. 6) relative to the axisof symmetry S and the orientation of the test probe 40 (characterized bythe inclination angle Phi relative to the insonification plane P).

While the inspection method is carried out, the solid shaft 100 isrotated, by means of a rotating device which is not shown, by 360° or anintegral multiple thereof about its axis of symmetry S, which coincidesin FIG. 6 with the X axis. The rotation angle of the solid shaft aboutits axis of symmetry is in this case referred to as Beta; it is acquiredby means of a suitable angle encoder (not shown). At a fixed X positionof the test probe 40, the entire range of the insonification angle Thetaaccessible by means of the test probe 40 is electronically tuned forevery rotation angle Beta by means of the control unit 20. For eachindividual insonification angle Theta, the echo signal is recorded in atime resolved manner and digitized in the selected travel time intervalI (Theta). The data points thus obtained can be plotted in a diagramaccording to FIG. 4. That is, from the entirety of the recorded echosignals, those are being selected, with regard to time, that correspondto the selected ROI. These echo signals are then digitized, i.e. a setof data points to be analyzed are generated for a given insonificationangle Theta.

To each individual point w on the surface of the solid shaft 100, anecho value G (w) is assigned which corresponds to the maximum signalfrom the ROI as-signed to this point. If this method is carried out fora plurality of rotation angles Beta, which can, for example, be gonethrough gradually in steps of 0.5 to 1° up to a total rotation angleBeta of at least 360°, then it is possible to plot the signal valuesobtained into a so-called C image. In such a C image, the signal valueassigned to an echo signal is plotted into a diagram according to FIG.5, in which, for example, the insonification angle Theta is used as theabscissa and the rotation angle Beta of the solid shaft 100 as theordinate. In this case, the echo value G can be coded, for example, bymeans of brightness values or in color. A three-stage scale was used inFIG. 5. If an echo value G remains below a registration limit, then thispoint is marked brightly in the C image according to FIG. 5. If itexceeds a registration limit but does not yet have to be assigned to aflaw size that is considered critical, then it is coded with a second(e.g. darker, e.g. orange) color value. Finally, if the echo value Gexceeds a value that is assigned to a critical flaw size, it is codedwith a third color value, e.g. in the signal color red. A diagramaccording to FIG. 5, which results in this way, already has a highinformative value for an expert user of a device according to theinvention.

The interpretability of the result according to FIG. 5 is improved yetagain if it is not the insonification angle Theta that is used as theabscissa, but the X position (position relative to the axis of symmetryS of the workpiece) of the point w on the workpiece surface assigned tothe ROI. The representation that results in this manner substantiallycorresponds to the representation according to FIG. 5, but is suitablefor a direct transfer onto the three-dimensional representation of theexamined solid shaft 100 of FIG. 6 generated according to the invention.The color-coded signal values are then plotted on the surface of thethree-dimensionally represented workpiece depending on the rotationangle Beta of the shaft 100 and on the position on the axis of symmetryof the shaft 100 (position on the X axis). The result is the flawrepresentation apparent from FIG. 6, which has an enormously improvedinterpretability over the visualization methods known so far from theprior art.

Particular advantages also result, in particular, when therepresentation according to FIG. 6 is designed in such a way that arotation of the shaft 100 about its axis of symmetry S can be shown.This is possible, for example, in a CAD model of the solid shaft 100with the echo values G (w) plotted in a spatially resolved manner on itssurface. A moving representation of the rotation of the solid 10 shaft100 about the rotation angle Beta as a sequence of individual imagesthat combine into a film is also conceivable, and protection is soughttherefor.

What is claimed: 1-20. (canceled)
 21. A method for near-surface,non-destructive inspection of a workpiece by ultrasound, the methodcomprising: insonifying a plurality of ultrasonic test pulses at adefined insonification angle into a rotationally symmetric workpiece ata surface coupling location via a phased array test probe coupled to theworkpiece; recording a plurality of ultrasonic echo signals from theworkpiece, each of the plurality of ultrasonic echo signals respectivelycorresponding to each of the plurality of ultrasonic test pulsesinsonified via the phased array test probe; selecting a travel timeinterval associated with a sound path of each of the plurality ofultrasonic test pulses, the selected travel time interval correspondingto a near-surface region of the workpiece; generating an echo value foreach of the plurality of ultrasonic echo signals by analyzing theplurality of ultrasonic echo signals in the selected travel timeinterval; and generating a representation of the near-surface region ofthe workpiece, wherein the echo value is depicted in the representationin a spatially resolved manner.
 22. The method according to claim 21,wherein the representation of the near-surface region of the workpieceis two-dimensional or three-dimensional.
 23. The method according toclaim 21, wherein a point at which an echo value is depicted in therepresentation of the workpiece is assigned to a sound path of anultrasonic test pulse in the workpiece.
 24. The method according toclaim 21, wherein the plurality of ultrasonic echo signals in theselected travel time interval are subjected a travel time-dependentand/or an insonification angle-dependent amplification.
 25. The methodaccording to claim 21, further comprising repeating the steps ofinsonifying, recording, generating an echo value, and generating arepresentation in one or more fixed surface coupling locations.
 26. Themethod according to claim 25, wherein a mean value of the generated echovalues is determined and presented in a spatially resolved manner in therepresentation.
 27. The method according to claim 21, wherein the traveltime interval is selected in such a way that the ultrasonic test pulsereaches the near-surface region of the workpiece within the travel timeinterval.
 28. The method according to claim 21, wherein the plurality ofultrasonic test pulses are insonified into the workpiece via placementof the phased array test probe at a plurality of surface couplinglocations relative to an axis of symmetry of the workpiece, theultrasonic test pulses insonified into the workpiece at differentinsonification angles and further wherein steps a-e are carried out foreach of the plurality of ultrasonic test pulses.
 29. The methodaccording to claim 21, wherein the sound path of the insonifiedultrasonic test pulses and an axis of symmetry of the rotationallysymmetric workpiece share a common insonification plane.
 30. The methodaccording to claim 29, wherein the plurality of ultrasonic test pulsesare insonified into the workpiece such that the common insonificationplane rotates about the axis of symmetry of the rotationally symmetricworkpiece.
 31. The method according to claim 30, wherein the commoninsonification plane is rotated by an integral multiple of 360°.
 32. Themethod according to claim 21, wherein the plurality of ultrasonic testpulses are insonified into the workpiece such that a travel direction ofa first part of the ultrasonic test pulses has a first component in thesame direction as the axis of symmetry of the workpiece, and the traveldirection of a second part of the ultrasonic test pulses has a secondcomponent oriented contrary to the direction of the axis of symmetry ofthe workpiece.
 33. The method according to claim 21, wherein theworkpiece has an anisotropic sound velocity for ultrasound.
 34. Themethod according to claim 21, wherein the workpiece is a forged solidshaft.
 35. A testing device for near-surface, non-destructive inspectionof a workpiece by ultrasound, the testing device comprising: a phasedarray test probe for insonifying a plurality of ultrasonic test pulsesat a defined insonification angle into a rotationally symmetricworkpiece having a diameter that changes from section to section and forrecording a plurality of ultrasonic echo signals from the workpiece; anda control unit, operatively coupled to the phased array test probe andconfigured to cause the phased array test probe to insonify theworkpiece and record a plurality of ultrasonic echo signals from theworkpiece, wherein the controller is configured to select a travel timeinterval corresponding to a near-surface region of the workpiece and togenerate a representation of a near-surface region, the representationincluding a plurality of spatially resolved echo values determined basedon analyzing the recorded ultrasonic echo signals in the selected traveltime interval.
 36. The testing device according to claim 35, wherein theplurality of ultrasonic test pulses reach the near-surface region of theworkpiece within the selected travel time interval.
 37. The testingdevice according to claim 35, further comprising a guiding deviceconfigured to orient the phased array test probe relative to an axis ofsymmetry of the workpiece such that a sound path of the insonifiedultrasonic test pulses and the axis of symmetry of the workpiece span acommon insonification plane.
 38. The testing device according to claim35, wherein the phased array test probe comprises a plurality ofultrasonic transducers divided into a plurality of individuallycontrollable transducer segments, and the control unit is furtherconfigured to cause the transducer segments to insonify the workpiece atdifferent insonification angles via the plurality of ultrasonic testpulses.
 39. The testing device according to claim 35, further comprisinga rotating device configured to cause the workpiece to be rotated aboutan axis of symmetry relative to a position of the phased array testprobe.
 40. The testing device according to claim 35, wherein the phasedarray test probe comprises a first ultrasonic transducer and a secondultrasonic transducer, and a first travel direction of a first pluralityof ultrasonic test pulses insonified into the workpiece via the firstultrasonic transducer relative to an axis of symmetry of the workpieceis oriented contrary to a second travel direction of a second pluralityof ultrasonic test pulses insonified by the second ultrasonic transducerinto the workpiece.